Nothing says jarring like people in tuxes and gowns praising unions and singing lines like “there’s something so damned low about the rich!”

This odd juxtaposition takes place at City Center, where Marc Blitzstein’s 1937 “The Cradle Will Rock” opened the new series Encores! Off-Center last night.

This being a concert version, the cast — led by Broadway faves Raúl Esparza, Anika Noni Rose, Danny Burstein and Judy Kuhn — is in evening wear. But even in black tie, the musical’s radical spirit occasionally burns through.

“Cradle” bothered people right from the start. Even its sponsor, the WPA, tried to put the kibosh on the opening, worried about a show advocating a worker uprising against corrupt fat cats.

Undeterred, the company performed backed solely by Blitzstein at the piano. This and the composer’s modernist style helped establish “Cradle” as America’s answer to “The Threepenny Opera.”

This version, directed by Sam Gold (“Picnic,” “Seminar”), is an interesting hybrid. On the one hand, an onstage 14-piece band performs Josh Clayton’s new arrangements — more intimate than Blitzstein’s original orchestrations, but obviously more lush than the spare piano version we usually hear.

On the other, the stark staging is a throwback to both the initial “Cradle” and the way Encores! used to be: There aren’t any sets; the actors, script in hand, stay seated and step up only to sing.

Some of Gold’s more daring moves don’t quite pay off, like casting Kuhn as a cigar-chomping newsman and 10-year-old Aidan Gemme as a cop and a professor. Both actors do their best, but the ploy feels distracting — and Kuhn’s a lot better when she returns as an immigrant’s wife.

Likewise, Esparza’s a little too polished to be entirely believable as the charismatic Larry Foreman, “who goes around stormin’ and organizin’ unions.” When Foreman calls for smashing the established order, you’re not quite inspired to follow him down to the break room, let alone up the barricades.

Still, the cast is in fine voice and some great moments make up for the weaknesses.